Load planning, vehicle routing as a heuristic problem, and carrier selection.
3 questions in Logistics & Supply Chain.
Triage before optimisation: classify what is already committed, what can still be diverted and what has not shipped, then reallocate the scarce alternative capacity by business priority rather than by cost. It only works if your model holds legs and alternates rather than a single route with a port baked into it.
Usually nothing is wrong with the solver: it is optimising against a model missing constraints the planner knows and never told it, so the plan is optimal and unrunnable. The fix is to capture the overrides as data and turn the recurring ones into constraints, rather than to improve the objective.
You stop pursuing optimality and engineer for a wall-clock budget: build a feasible plan with a construction heuristic, improve it with local search or a metaheuristic until the clock runs out, and model the constraints that genuinely bind, which are time windows, capacity and statutory driver hours.